仅删除第一次和第三次出现的块的内容 [英] Remove the contents of block only 1st and 3rd occurence

问题描述

以下sed删除了{content-start}和{content-end}之间所有出现的块，但只想删除第1和第3块，而不是第2块.

Below sed removes all occurrences of blocks between {content-start} and {content-end}, but want to remove only 1st and 3rd blocks and not 2nd block.

sed -ie '/{content-start.*}/,/{content-end}/d' test.txt

test.txt:

{content-start}
abc1
def1
ghi1
{content-end}
{content-start}
abc2
def2
ghi2
{content-end}
{content-start}
abc3
def3
ghi3
{content-end}

推荐答案

sed用于单个行上的简单替换，即s/old/new/，全部.对于其他任何事情，您都应该使用awk:

sed is for simple subsitutions on individual lines, i.e. s/old/new/, that is all. For anything else you should be using awk:

$ awk '{rec = rec $0 ORS} /{content-end}/{if (++cnt == 2) printf "%s", rec; rec=""}' file
{content-start}
abc2
def2
ghi2
{content-end}

或者如果您想对单独的行进行任何操作，则将记录的每一行保存在数组中，而不是将整个记录保存为字符串:

or if you're ever going to want to do anything with individual lines then save each line of the record in an array rather than saving the whole record as a string:

{ rec[++numLines] = $0 }
/{content-end}/ {
    if ( ++cnt == 2 ) {
        for (lineNr=1; lineNr<=numLines; lineNr++) {
            print rec[lineNr]
        }
    }
    delete rec
    numLines = 0
}

以上内容适用于任何UNIX系统上任何shell中的任何awk，并且在/当您的需求发生变化时，可以轻松地进行增强.

The above will work with any awk in any shell on any UNIX system and is trivial to enhance if/when your requirements change.

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